The invention relates to a lost foam casting system, and more particularly to an improved method and apparatus for introducing molten metal to the pattern assembly.
Lost foam casting is a known technique. A pattern assembly formed of evaporative foam material, for example gasifiable or liquifiable expanded polystyrene, or expanded polymethylmethacryate (PMMA), either of which which may be coated with a thin ceramic coating, is placed in a flask and surrounded by unbonded particulate media, most commonly sand, though other particles can be used such as zirconia, metal spheres, etc. Upon application of molten metal to the pattern assembly, the foam material vaporizes and is replaced by the metal in the shape of the pattern assembly. The vaporized foam material escapes into the interstices in the sand.
The pattern assembly typically includes one or more workpieces of given respective patterns for yielding cast metal parts, and a sprue connected by one or more in-gates to the workpieces for communicating the molten metal through the sprue to the in-gates and then to the workpieces. After cooling, the cast metal sprue and the in-gates are broken away from the workpieces and discarded or recycled. The cast metal workpieces are then trimmed to yield the final product.
The present invention arose out of efforts to provided improved case aluminum alloy cylinder heads and engine blocks for internal combustion engines in marine applications, and cast steel two cycle outboard crankshafts, though the invention is not limited thereto.
In the present invention, molten metal is applied to the foam pattern assembly by vacuum lift. Vacuum is applied through the sand, and a gas-permeable member or path is provided communicating between the sand and a vertical fill passage such that molten metal is vacuum lifted to the foam pattern assembly.